• I would put the silicone around the face plate but leave a small gap at the very bottom to allow any water that does get behind the plate to drain away. If the faceplate has a inside lip, you can put the silicon against it on the inside and it will not show. But be sparing. You just want to direct the water around the outside of the plate and down the wall to the shower drain rather than letting it go under the plate and inside the wall. I'm assuming the valve underneath the plate sticks out of a "hole" in the wall and if not covered would allow water inside the wall. And that it is below the shower head and not on another wall that doesn't get water (that's the way ours is set up.)

I have a Delta shower valve I bought about a year ago and it is not designed to have any silicon to seal it to the wall. The back of the faceplate has a soft rubber seal on the back in an arc along the top and down the sides, kind of like an upside down horseshoe. When you tighten the screws in place this seal is tightened against the shower wall, so that water would just run around the seal to the bottom of the faceplate and run out. The bottom of the plate is not sealed to the wall. I assume you could get the same results with with silicon sealer.

Bruce